Overspeed-prevention mechanisms are typically integrated into vehicular diesel engines to protect the engine from operating at speeds above a set limit. Such limits may be in place to prevent the vehicle from traveling above a certain speed, prevent runaway acceleration, or engine over-revving.
Overspeed-shutdown mechanisms known in the prior art utilize a means for detecting the overspeed condition and, upon detection, a means for remedying the overspeed condition (e.g., by eliminating air in the air-intake manifold, or eliminating fuel to the engine).
One example of an overspeed-shutdown mechanism is described in U.S. Pat. No. 4,282,838 (the '838 patent), wherein a flyweight mechanism acts to activate a valve that in turn shuts off air to the intake manifold when the engine is in an overspeed condition.
Typically, a reset lever must be manually actuated to reverse the overspeed-shutdown mechanism. For example, in the '838 patent, after the overspeed-shutdown mechanism has been activated, in order to restore engine operation, a lever must be moved to release the shutoff valve blocking the air intake manifold.
A diagrammatic illustration of a prior art overspeed-shutdown mechanism 61 attached to an engine 55 is illustrated in FIG. 1. The engine 55 receives air provided by an air source 60 (e.g., the compressor of a turbocharger) through the air-intake manifold 57. Airflow is illustrated as arrows in FIGS. 1, 3A, and 3B. If an overspeed event occurs in the engine 55, the overspeed-shutdown mechanism 61 acts to shut down the engine 55. For example, mechanism 61 actuates a valve 62 which closes air-intake manifold 57, resulting in a loss of combustion air to the engine 55, thus precluding internal combustion and shutting down the engine 55.
A typical process flow for an air-intake overspeed-shutdown mechanism (e.g., as illustrated in FIG. 1) is illustrated in the flow chart of FIG. 2. The overspeed-shutdown process 100 begins with a step 105 wherein the engine speed exceeds a predetermined limit. When the predetermined speed is exceeded, a step 110 is implemented whereby the overspeed-shutdown function is automatically activated. The overspeed-shutdown process 100 continues with a step 115 wherein the output to the overspeed-shutdown valve is activated, thus closing off air intake to the engine. As a result of air being cut off from the engine, the engine shuts down in step 120. This ends the overspeed-shutdown process 100.
After an overspeed-shutdown mechanism has been activated, the engine will not operate. For example, after an air-intake shutdown has occurred, no air will be allowed into the engine, fuel will not combust, and the engine will not start. Without knowledge of an overspeed shutdown occurrence, the user of a shut-down engine may erroneously believe that a mechanical failure has occurred elsewhere in the engine without realizing that the overspeed-shutdown mechanism has been activated. A common response of a user in such a situation is to turn the key of the vehicle to engage the starter, so as to restart the engine. However, without air being allowed into the engine, the starter will turn over, yet the engine itself will not start. Damage to the starter system may result from repeated attempts at starting when the overspeed-shutdown mechanism has been activated and not reset.
Additionally, possible damage to the engine as a result of a vacuum shutdown is not limited to just the starter system. A diesel engine is designed to contain an explosion and harness its energy, not hold a vacuum. The internal components are biased/optimized for the engine's primary task. Thus, damage to engine components may result from allowing the engine to continue to pull a vacuum against a blockage.
What is desired, therefore, is a method and system for detecting when an overspeed-shutdown mechanism has been activated in a vehicular internal combustion engine, such information can be used to protect a vehicular starting system by preventing its engagement when such an overspeed shutdown condition exists.